This invention pertains to telecommunications, and particularly to generation and handling of frames for single-frequency networks
In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units (UE) such as mobile telephones (“cellular” telephones) and laptops with wireless capability (e.g., mobile termination), and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data via radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called “NodeB” or “B node”. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions (particularly earlier versions) of the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
Specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are ongoing within the 3rd Generation Partnership Project (3GPP). The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE).
Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected directly to a core network rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller (RNC) node are performed by the radio base station nodes. As such, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes.
The evolved UTRAN (E-UTRAN) comprises evolved base station nodes, e.g., evolved NodeBs or eNodeBs or eNBs, providing evolved UTRA user-plane and control-plane protocol terminations toward the user equipment unit (UE). The eNB hosts the following functions (among other functions not listed): (1) functions for radio resource management (e.g., radio bearer control, radio admission control), connection mobility control, dynamic resource allocation (scheduling); (2) selection of a mobility management entity (MME) when no routing to an MME can be determined from the information provided by the user equipment unit (UE); and (3) User Plane functions, including IP Header Compression and encryption of user data streams; termination of U-plane packets for paging reasons, and switching of U-plane for support of UE mobility. The eNB hosts the PHYsical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. The eNodeB also offers Radio Resource Control (RRC) functionality corresponding to the control plane. The eNodeB performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated UL QoS, cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of DL/UL user plane packet headers.
Inband relays are being discussed in 3GPP for future LTE releases. As shown in FIG. 1, an inband relay involves a donor base station node sending subframes of information using a given frequency band and over an air interface to a relay node. The link between the donor base station node and the relay node has been referred to as the backhaul link. The relay node in turn uses the same frequency band to send subframes of information to a wireless terminal (UE).
The in-band relay configuration requires the relay node to have antennas that are receiving subframes on a downlink from the donor base station node while also having antennas that transmit subframes on a downlink to the wireless terminal (UE). Since both the reception from the donor base station node and the transmission to the wireless terminal (UE) involve the same frequency band, a problem with inband relays is avoidance of self-interference from transmitting antennas to receiving antennas in the relay node.
Time multiplexing between the backhaul and access links has been proposed as an approach to solving the self-interference issue. However, a problem with time multiplexing is that 3GPP specifications allow wireless terminals (UE) to normally assume that the base station transmits certain physical signals in each subframe, meaning that the relay node needs to transmit in each subframe.
Multicast/broadcast single-frequency network (MBSFN) operation involves simultaneous transmission of the exact same waveform from multiple cells, over a single frequency. In this way the wireless terminal (UE) receiver perceives the multiple MBSFN cells as one large cell. Also, instead of inter-cell interference from neighboring cell transmissions, the wireless terminal experiences constructive superpositioning of the signals transmitted from multiple MBSFN cells.
It has been proposed in 3GPP to assign and signal some subframes as so-called “MBSFN” subframes. The definition of the MBSFN subframe pattern is included in the System Information Block Type 2 (Specified in 3GPP document 36.331, “Radio Resource Control (RRC) Protocol Specification”). Signaling some subframes as “MBSFN” subframes has the effect of telling the wireless terminal (UE) that only a control region of those subframes is transmitted. The portion of those “MBSFN” subframes that is not transmitted from the relay node can then be used for downlink communication over the backhaul link. MBSFN subframe patterns can be configured with different periods, for instance 10 and 40 ms periods are possible.
The possibilities for specifying some subframes as “MBSFN” are limited. Each 10 ms radio frame consists of 10 subframes numbered 0 . . . 9. Moreover, in Frequency-Division Duplex (FDD) mode only subframes 1, 2, 3, 6, 7, 8 can be marked as “MBSFN”. In a Time-Division Duplex (TDD) mode, only subframe numbers 2, 3, 4, 7, 8, 9, can be marked as “MBSFN” subframe.
In an FDD system, the LTE Hybrid Automatic Request for Retransmission (HARQ) transmission scheme is (to a large extent) designed with the intent of an 8 ms (8 subframes) periodic operation. In particular, as shown by way of example in FIG. 2, uplink HARQ retransmissions are always performed an integer multiple of 8 ms after the original transmission, generating a desired uplink transmission pattern of period 8 ms. Furthermore, downlink signals that are needed to support uplink transmissions (scheduling grants and HARQ ACK/NACKs) need to be transmitted 4 subframes before or 4 subframes after the corresponding uplink transmission, generating a similar desired downlink transmission pattern of period 8 ms. Further, for each downlink transmission, a corresponding ACK/NACK is transmitted in the uplink 4 subframes later.